docs: def find_group(self, star, starlist):
          """
          Find the ids of those stars in ``starlist`` which are at a
          distance less than ``crit_separation`` from ``star``.
  
          Parameters
          ----------
          star : `~astropy.table.Row`
              Star which will be either the head of a cluster or an
              isolated one.
          starlist : `~astropy.table.Table`
              List of star positions. Columns named as ``x_0`` and
              ``y_0``, which corresponds to the centroid coordinates of
              the sources, must be provided.
  
          Returns
          -------
          Array containing the ids of those stars which are at a distance less
          than ``crit_separation`` from ``star``.
          """
  
          star_distance = np.hypot(star['x_0'] - starlist['x_0'],
                                   star['y_0'] - starlist['y_0'])
          distance_criteria = star_distance < self.crit_separation
          return np.asarray(starlist[distance_criteria]['id'])